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Comment by h2odragon | Hacker News Reader

$200ea @q1: https://www.sparkfun.com/products/21287

> 37-138 MHz (downlink), 148-150 MHz (uplink)

Makes me wonder how this deals with local noise. There's rather a lot of extant traffic in that range already and its worst in populated areas; even rural tho there's going to be things wandering by that speak loud in that range.

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Might be using a digital mode designed for weak signal communications. I'm not familiar with what might be used commercially but in amateur radio FT8 is popular and amazing. I live in a neighborhood with ~900 homes, restrictions on antennas, and quite a high noise floor. On 20m wavelength (granted, quite different from the 2m λ of this modem) with a center fed dipole antenna (SWR 1.5) that is 2m off the ground (not good for long distance because the ground reflects most of the radiated energy is up rather than out) and transmitting at 100 watts, I can send and receive messages 17700km (11000 miles). Using regular analog voice instead of FT8, I get about 3200km (2000 miles) with the same setup. Those distances are on the surface of the earth. The actual radio signal is traveling a bit further because it bounces between Earth and ionosphere as it travels. For this modem, the signal would be traveling line-of-sight and probably less than 1000km?

> restrictions on antennas

Assuming you’re in USA, what you need is a tower with “An antenna that is designed to receive local television broadcast signals.”

https://www.fcc.gov/consumers/guides/installing-consumer-own...

Interesting :)

Could you try with QRP 5watts to see how far you can reach? 11K miles on 100w is not that impressive?

It’s impressive, to me at least, given the antenna is in an NVIS configuration (configured for distances of ~1k miles) and given that anything below S7 is in the noise. I have tried QRP and cannot reach overseas with this antenna placement.

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